Moving Mailboxes between Forests/Domains

We are doing a total domain migration after experiencing numerous, never-before-seen problems with our AD (problems that Microsoft told us we were out of luck on). As part of this process we need to move all mailboxes to the new domain. To our understanding this is best done with either the Exchange Migration Tool or ExMerge. We have had little success with either. Does anyone know the best order in which to use ADMT 3.2, Exchange Migration Tool and/or Exmerge to move mailboxes between forests and servers?

Here is some more information regarding our network:
Exchange 2003
AD is fully 2008 R2
Everything is running (in relation to this problem) on VMware ESX/ESXi
Domain name of old domain is 'companynameglobal.com'
Domain name of the new domain is 'companyname.lcl'
The DNS suffix we use for all our email addresses is 'companyname-global.com' (Notice the hyphen)
Notice that these are not in the same forest at all
The 2 forests are setup with a 2-way external non-transitive trust
We've followed ADMT steps and haven't had any problems that we need help with in the ADMT process
DNS conditional forwarders have been setup between domains and all DNS routing is working just fine
The Exchange servers are not configured to route mail between them at all

We need any solution (that doesn't include buying Quest Software's $$$ solution) that will allow us to migrate as transparently as possible across these domains/forests. As we have only a small staff overseeing 100+ users (many of them remote) we won't be able to tolerate a large scale (big downtime) transition.

If we migrate the mailbox first using ExMerge then we have a problem because the user won't receive any mail on their account has this server that we're moving to isn't tied into the mail flow that comes in from the internet. As we have 100+ users this isn't an option UNLESS we can have the other server (on another forest) tied into the mail flow. If that is possible that is great, we just need to know how to set it up.

If we migrate the user and then try and move the mailbox over with Exmerge it keeps the old Exchange server as its Exchange 'home server' and we're unable to upload to it's mailbox on the new Exchange server because it doesn't have one.

I believe you can enter the IP of the new Exchange server in your current SMTP virtual server properties>Messages tab>"forward all mail with unresolved recipients..." setting, so this way inbound mail flow will remain the same but migrated accounts will still be able to receive email until all accounts migration (and external mail routing) is complete.

It's been a long time since I've done a migration so perhaps someone else can verify, but you can perform a test with a dummy account to verify.

I tried sending this user "Jon Smith" an email while he was on the new Exchange server on the new and seperate forest from both my internal account (resident on the other forest's exchange server) and from my gmail account with the the "forward all mail with unresolved recipients" setting both off and on.

These were my results:

Sent internally with "forward all mail with unresolved recipients" filled out to the server on the other forest: success
Sent internally with "forward all mail with unresolved recipients" blank: success
Sent from Gmail to Jon Smith while "forward all mail with unresolved recipients" setting blank AND/OR filled out correctly: failure with the below message:

This tutorial will walk an individual through locating and launching the BEUtility application to properly change the service account username and\or password in situation where it may be necessary or where the password has been inadvertently change…

This tutorial will show how to configure a single USB drive with a separate folder for each day of the week. This will allow each of the backups to be kept separate preventing the previous day’s backup from being overwritten.
The USB drive must be s…